Packaged magnesium anode with compacted backfill



Oct. 24, 1950 R. M. HUNTER 2,527,361

PACKAGED MAGNESIUM ANoDE WITH coMPAcTED BACKFILL Fild Oct. 22. 1948 Magnesium anca/ Mge INVENTOR. v @040/7 M. Hun /er BY Patented Oct. 24, 1950 PACKAGED MAGNESIUM AN ODE WITH COMPACTED BACKFILL Ralph M. Hunter, Midland, Mich., assignor vto The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application October 22, 1943, Serial N0. 55,854

4 Claims. (Cl. .2M-.197)

This invention relates to improved packaged anodes for the galvanic protection of underground metals. It also concerns a method of making them.

In the galvanic protection of pipelinesV and other underground structures, sacrificial electrodes of a metal anodic to the structure, such as magnesium, are buried in the earth near the structure and are connected to it by electrical conductors. The resulting flow of current maintains the structure cathodic with respect to the soil and greatly Vminimizes its corrosion. When using magnesium in this service, it is customary to bury it in a prepared bed or backll designed to control the chemical nature of the anode environment. y y

In making cathodic protection installations, usual practice has been to transport the sacricial anodes and the backll ingredients separately to the site. Each anode isV then sunk in a hole dug for the purpose, after which the backll ingredients are mixed and tamped around the anode. This' procedure, while eifective, is extremely cumbersome. Efforts have therefore been made to develop a packaged anode, i. e. a prepared package containing an anode with the proper quantity of appropriate backll already in place around it. Such a packaged anode could, of course, be installed very readily simply by burying it in the earth.

Two principal types of packaged anodes have been proposed heretofore; neither has been fully satisfactory. In one, the anode is centered in a water-permeable container which -alsoholds thev backll in powdered form. Except with expensive sacks of special design, the containers have proved sub-ject to puncture during transportation or the anodes have often shifted out of their required central position in the backll. In

the yother type, the anode is embedded in a mass,

of backll cemented together by a bonding agent. With this form, extreme" vcare in installation is required to obtain good electrolytic contact with the earth since the backfill is held fixed in shape by the cement and is not free tovshift about or to expand to conform to irregularities of the hole in which it is placed.

In view of these diiiiculties it is the principal object of the present invention to provide an improved packaged anode which is not subject to the disadvantages mentioned.

The invention will :be explained with reference to the accompanying drawing in which Fig. 1 is a schematic elevation, partly in section, showing one method of making the new anode, and

Fig. 2 is an elevation, largely in section, showing one manner of using the new packaged anode in the galvanic protection of a buried pipeline.

In the packaged anodes of the invention, the

magnesium metal anode is embedded in a selfsustaining compacted mass of a comminuted nonacidic solid electrolyte held together solely by the adhesive forces resulting from the compaction. As long as this assembly stays dry, the anode remains encased in a body of somewhat porous stone-like material which is of such composition and size as to provide a suitable electrolytic environment for the anode and which is suiciently strong to withstand handling. However, soon after the packaged anode is installed in moist earth, the backfill softens enough to conform to the hole in which is it installed. W

In so far as known, any granular or powdered non-acidic solid electrolyte may be used in making the new packaged anodes, since the major function of this material is simply to render the backll electrolytically conductive. In general, alkaline earth metal hydroxides and alkalior alkaline-earth metal salts of acids which form water-soluble magnesium salts, or mixtures of these substances, are preferred. It is particularly advantageous to select an electrolyte which is only sparingly soluble in water, i. e. one having a solubility of from about 0.1 to about 2 per cent by Weight at atmospheric temperatures. `Cal cium sulfate, usually in the form of gypsum (CaSO4.2H2O), is perhaps the best choice because of its low cost and excellent performance, although magnesium suliite is also Very satisfactory. (The latter is claimed in a co-pending application Serial No. 745,451, filed May 2, 1947, by H. A. Robinson.) v`

In addition to electrolyte, the compacted backi'lll for the new packaged anodes may also have mixed uniformly throughout minor proportions of other non-acidic materials, e. g. sand, gravel, crushed washed coke, and other electrolytically inert fillers. Granular magnesium hydroxide or oxide may be added, each having the desirable effect of assisting in maintaining alkalinity. Powdered or granularbentonite (montmorillonite, asodium-type colloidal clay) is also advantageous in that it tends to improve absorption a'nd retention of water and to retard leaching -of the electrolyte.

Of the backll compositions useful in the invention, mixtures of granular gypsum and granular bentonite are preferred. One of these', which is particularly desirable because' ofh'its rapid-wetting characteristics, `is a mixture of about parts by weight ground gypsum, 5 parts of `sodium sulfate, and 20 parts of ground bentonite. (This composition is claimed in a copending application Serial No. 982, filed January 7, 1948 by M. O. Robinson et al., now Patent No. 2,480,087.) y

In making the packaged anodes of the invention a magnesium metal anode is embedded in a loose mass of a comminuted backll composition of the type just described, the whole being confined in a mold. The mass is then subjected to a pressure of at least one ton per square inch to compact the backfill into a self-sustaining body encasing the anode. With some backlls,4 best results are obtained by first moistening the mass to be compacted to insure maximum adhesion.

A typical procedure is illustrated in Fig. 1, in which a magnesium anode 3 is being encased in a granular backll composition 4. As there shown, the anode 3 is made of an elongated cylindrical body of magnesium cast around a core formed by part of a steel cable 5, the other portion of which extends beyond the anode to constitute an electrical lead-wire. The anode is embedded centrally in the backll Il to be compacted which in turn is confined in a split cylindrical mold 6 of inside diameter such as to provide ample backll around the anode. The mold may be closed at the top by a closely-fitting retractable circular dummy-block I having a small central opening 8 for the lead-wire 5. Force may be applied to the block 1 by a ram 9 provided in its lower face with a radial groove I8 through which th'e lead-Wire 5 may pass. The block I is held to the ram 9 by countersunk screws 'I'.

In operation, the ram 9 is forced against the block 1, compacting the backfill Il about the anode 3. Movement of the ram is continued until a pressure of one ton per square inch or more is developed in the backll, after which the assembly is allowed to dwell under the pressure for a short period. The block I and ram 9 are then retracted and the mold E is split to release the packaged anode.

Some further protection to the compacted backll may be provided by wrapping the assembly in cloth, either after compaction or by initially placing the cloth in the mold. If the packaged anode is likely to be stored or shipped under damp conditions, it is best to enclose it in a moisture-proof bag until the time of use.

A tyical installation for cathodic protection, using the packaged anode of the invention, is shown in Fig. 2, in which a steel pipeline I I buried in the earth is being protected. As shown, the packaged anode is buried in the ground near the pipeline with the lead-wire 5 being connected electrically to the pipeline by a conductor I2. The latter is brazed to the pipe and connected to the wire 5 by a joint I 3. All wiring is preferably insulated.

In making the installation, it is necessary simply to dig a hole I4 the size of the packaged anode, insert the entire package, tamp the earth over it, and make the electrical connection. In dry weather, it is desirable to pour water into the hole I4 to hasten the start of electrolytic action. As soon as the packaged anode is in place, moisture from the soil enters the pores which are present in the backfill even after its compaction and electrolysis starts. As absorption of soil moisture continues, the backll gradually disintegrates or exfoliates, swelling somewhat and lling the hole I4 completely.

In field use of the invention, the number and size of anodes and the optimum quantity of backll per anode for effective protection of a givenl pipeline or other structure are determined by well-known principles.

While the invention has been described as useful in the cathodic protection of underground ferrous metal, it is applicable in protecting structures of any corrodible metal cathodic to magnesium. The sacricial anodes may be made either of magnesium or a magnesium-base alloy, both being comprehended by the term magnesium meta as used herein. I

What is claimed is: I

1. A packaged anode for use in cathodic pro- I tection systems comprising a magnesium metal anode embedded in ay self-sustaining compacted l mass of a granular electrolyte selected from the I class consisting of alkaline earth metal hydrox- I ides and alkaliand alkaline-earth metal salts of acids which form water-soluble magnesium salts held together solely by the adhesive forces resulting from compaction at a pressure of at I least one ton per square inch.

2. A packaged anode for use in cathodic prol tection systems comprising a magnesium metal I anode embedded in a self-sustaining compacted I mass consisting essentially of granular gypsum I and granular bentonite held together solely by I I I I I I the adhesive forces resulting from compaction at a pressure of at least one ton per square inch.

3. The method of making a packaged anode for use in cathodic protection systems which comprises embedding a magnesium metal anode in a loose mass of a granular electrolyte selected from the class consisting of alkaline earth metal hydroxides and alkaliand alkaline-earth metal salts of acids which form water-soluble magnesium salts confined in a mold and subjecting the mass to a pressure of at least one ton per square inch to compact the electrolyte into a self-sustaining body encasing the anode.

4. In combination with an underground structure of a corrodible metal cathodic to magnesium, a cathodic protection system comprising a packaged anode as defined in claim 1 inserted snugly in a preformed hole in the earth near the structure, the anode being connected electrically to the structure.

RALPH M. HUNTER.

- le of this patent:

UNITED STATES PATENTS Name Date Ruben June 10, 1947 OTHER REFERENCES Corrosion, vol. 1.l No. 2, June 1945, pages 67, 68.

Number 

1. A PACKAGED ANODE FOR USE IN CATHODIC PROTECTION SYSTEMS COMPRISING A MAGNESIUM METAL ANODE EMBEDDED IN A SELF-SUSTAINING COMPACTED MASS OF A GRANULAR ELECTROLYTE SELECTED FROM THE CLASS CONSISTING OF ALKALINE EARTH METAL HYDROXIDES AND ALKALI- AND ALKALINE-EARTH METAL SALTS OF ACIDS WHICH FORM WATER-SOLUBLE MAGNESIUM SALTS HELD TOGETHER SOLELY BY THE ADHESIVE FORCES RESULTING FROM COMPACTION AT A PRESSURE OF AT LEAST ONE TON PER SQUARE INCH. 